IDAHO GEOLOGICAL SURVEY TECHNICAL REPORT 12-4 MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG DIEDESCH, RODGERS, AND LINK

GEOLOGIC MAP OF PORTIONS OF THE PHI KAPPA MOUNTAIN, HYNDMAN PEAK, AND GRAYS PEAK QUADRANGLES, BLAINE AND CUSTER COUNTIES, T.F. Diedesch1, D.W. Rodgers1, and P.K. Link1 2012

MAP SYMBOLS DESCRIPTION OF MAP UNITS Contact - dashed where approximate, dotted where concealed ALLUVIUM (HOLOCENE) – Crudely stratified silt, sand, and Qal WOOD RIVER FORMATION, EAGLE CREEK MEMBER ELLA MARBLE (ORDOVICIAN) – Buff-weathering calc-silicate gravel deposited by present streams as channel or flood-plain Oe (Descriptions from Mahoney et al., 1991) marble. Forms prominent dip slopes. Upper part contains light-gray ? ? Fault - dashed where approximate, queried where uncertain materials; locally includes alluvial fan deposits. Description from to buff, thin- to medium-bedded marble with variable amounts of Dover (1983). WOOD RIVER FORMATION, MEMBER 6 (PENNSYLVANIAN- calcite, quartz, and calc-silicate minerals; mineralogical variations High-angle normal fault - dashed where approximate; ball PIPw6 7 PERMIAN) – Interbedded gray, buff- to brown-weathering, thick- emphasized by differential weathering. Siliceous partings and 26 COLLUVIUM (HOLOCENE) – Locally derived, incoherent Ok and bar on hanging wall bedded, fine- to medium-grained calcareous sandstone, calcarenite, quartzite interbeds increase in thickness and abundance toward the Qc accumulations of angular and poorly sorted rock debris; occurs as Oe and olive-brown, thick beds of fine-grained quartzite with interbeds contact with the overlying Kinnikinic Quartzite. Lower part is buff, Tei thin veneer or in talus cones along hill and valley sides; locally Low-angle normal fault - dashed where approximate; of laminated dark-gray to black carbonaceous and calcareous massive, more uniform and more coarsely crystalline and character- includes landslide deposits. Description from Dover (1983). half-circles on hanging wall siltstone. Crops out as rubbly, highly-fractured ledges on hillslopes istically crumbles to sand. Basal contact sharp and relatively concor- Os 60 40 41 and peaks. Contains fusulinids. Thicknesses approximately 1,700 m. dant. Thickness approximately 200 m. Description from Dover Strike-slip fault - dashed where approximate, dotted where TERRACE GRAVEL (HOLOCENE AND PLEISTOCENE) – (1983). 4851 Qt 48 Crudely stratified and poorly sorted gravel, sand, and silt in terraces 725 Ok 51 concealed; arrows show relative motion WOOD RIVER FORMATION, MEMBER 5 (PENNSYLVANIAN) – 39 41 727 standing as much as 30 m above present stream level; well-rounded IPw5 CLAYTON MINE QUARTZITE (ORDOVICIAN) – White, 37 Brown or olive brown, thick-bedded to massive, fine-grained Thrust fault - dashed where approximate; teeth on hanging clasts have a range of compositions reflecting that of drainage Oc 114°12’30” quartzite and calcareous quartz sandstone. Forms shelves abd vitreous, poorly sorted, thick-bedded to massive, micaceous and 42 patterns. Description from Dover (1983). wall benches throughout mid-elevations. Thickness 150-200 m. feldspathic gneissose quartzite; typically splits into slabs along mica 32 39 partings containing as much as 50% biotite; characterized by 36 Oe Wildhorse detachment fault - dashed where approximate, GLACIAL DEPOSITS, UNDIVIDED (PLEISTOCENE) – Boulder- well-developed coarse tabular cross-bedding. Contains some 48 DSla Qg WOOD RIVER FORMATION, MEMBER 4 (PENNSYLVANIAN) – 45 16 19 dotted where concealed; hachures on hanging wall rich, poorly sorted deposits present in most glaciated valleys; occurs IPw4 discontinuous layers and lenses of granule and pebble conglomerate 29 54 Carbonaceous and calcareous banded siltstone arranged in fining 724 10 in arcuate hummocky ridges representing terminal and recessional 49 upward cyclcic packages of micritic sandstone and silty micrite; with pink- to purplish-gray quartz clasts. Base generally concordant, 41 moraines, in linear patches of lateral moraine perched on valley Asymmetric anticline - axial trace; beds are upright, shorter complete Bouma sequences with base cut out; abundant sedimentary but locally slightly discordant and marked by about 2 m of quartz- 48 Pw7 Ok walls, and in irregular patches on cirque floors. Description from 50 arrow on steeper limb structures like tabular cross-lamination, convolute laminations, pebble conglomerate. Thickness about 300-425 m. Description from 48 Dover (1983). Oc 50 soft-sediment deformation; beds are laterally continuous with Dover (1983). Qg Asymmetric syncline - axial trace; beds are upright, shorter relatively sharp contacts. Thickness 250-200 m. 46 arrow on steeper limb Tcu CHALLIS VOLCANIC GROUP, UNDIVIDED (EOCENE) UNNAMED BANDED CALC-SILICATE (NEOPROTEROZOIC- CZbc CAMBRIAN) – Distinctively color-banded unit consisting of 7 WOOD RIVER FORMATION, MEMBER 3 (PENNSYLVANIAN) – 23 56 57 Qg RHYOLITE LAVA FLOWS – Discontinuous exposures of purple 40 Overturned syncline - axial trace, dotted where concealed; IPw3 Gray, typically pink- to purple-weathering, thin-bedded , platy alternating thin beds of various mineralogy. Relative proportions of 60 Tcr and lavender to yellow, flow-banded rhyolite. Crystals uncommon, arrows show dip direction of limbs limestone and shaly limestone. Locally, beds of interclastic limestone mineral constituents vary from band to band, and reflect primary but quartz and biotite are locally present. Maximum thickness 10 m. 71 at base of unit containing bioclastic grainstone, micrite, and chert- compositional layering in original sediment; rhythmically repeated 81 78 Granitic dike - Equivalent of Pioneer Intrusive suite granite pebble conglomerate of Hailey member. Contains fusulinids and sequences of compositional layers. Thickness of individual bands DACITE FLOWS – Gray to green-weathering, purple porphyritic 48 84 (Tei) 49 78 Tcd calcareous foraminifera. Thickness 75-200 m. ranges from a few millimeters to 15-20 cm; banding generally sharp Os dacite with abundant sanidine crystals. Upper part is finer-grained, and uniform and controls the characteristic splitting of the rock into Ok 4849 distinctly purple. Lower part is more coarsely crystalline and 722 Brecciated quartzite with sharp contact WOOD RIVER FORMATION, HAILEY MEMBER large slabs. Locally, soft sediment deformation disrupts composi- IPwh contains oxyhornblende in addition to sanidine. Weathers reddish- (Descriptions from Mahoney et al., 1991) tional layering. Basal contact sharp and generally concordant. 86 40 40 Strike and dip of inclined bedding - ball indicates top brown in places. Forms broad benches that define a flow foliation. Thickness about 100 m. Description from Dover (1983). New age 70 DSm 29 Thickness approximately 200 m. IPw5 85 26 direction known WOOD RIVER FORMATION, HAILEY MEMBER assignment from Link and Fanning (2009). IPw3/4 IPwh (PENNSYLVANIAN) – Contains Hall et al.’s (1974) Hailey 57 IPwh 37 PIPw6 71 Vertical bedding DACITE LAHAR – Gray to green-weathering with purple mottled- REFERENCES DSm 54 75 Tcl conglomerate and member 2. Lower cliff-forming unit of brecciated Oe porphyritic dacite clasts suspended in an ashy, greenish-gray matrix. Dover, J.H., 1983, Geologic map and sections of the central Pioneer Qg and sheared pebble conglomerate with subangular to rounded clasts 81 40 40 Clasts consist of fine-grained porphyritic dacite with abundant Mountains, Blaine and Custer Counties, Central Idaho: United States 60 Strike and dip of overturned bedding - ball indicates top 80 of quartzite, argillite, sandstone and chert; beds are tabular to lenticu- 48 47 Geological Survey Miscellaneous Investigations, Map I-1319, scale 48 ? direction known sanidine, plagioclase, and biotite crystals; enclaves within clasts are 82 lar and discontinuous, pinching out and possibly boudinaged along 72 common and consist of coarser-grained dacite fragments with 1:48,000. 61 40 major fault zones. Subordinate thin- to medium-bedded, fine- to 72 48 IPw3/4 ? 48 abundant sanidine crystals and less biotite than the fine-grained host. Durk, Kathleen, 2007, Geochronology of part of the Wildhorse Gneiss 722 Strike and dip of volcanic flow foliation coarse-grained sandstone. Upper member consists of blue-gray, 3171 I NW Tcu Os 3171 I NW Thickness approximately 125 m. Complex, Pioneer Moutains, Custer County, Idaho [Senior Thesis]: (PHI KAPPA MTN.) IPwh 79 (PHI KAPPA MTN.) 40 thin-bedded to massive, bioclastic grainstone and packstone, with ? Pocatello, Idaho State University, 38 p. 43°45’ 59 43°45’ Strike and dip of foliation 3171 II NW 40 3171 II NW micritic sandstone and siltstone; interfingers with chert-pebble (HYNDMAN PEAK) Qg 50 7 (HYNDMAN PEAK) DACITE PORPHRY – Blocky, reddish-brown-weathering silicified Hall, W.E., Batchelder, J.H., and Douglass, R.D., 1974, Stratigraphic 28 Tcp conglomerate. Bioclastic beds contain remnants of fusulinids, 39 porphyritic dacite with large, cm-scale grains of clay-altered section of the Wood River Formation, Blaine County, Idaho: U.S. 114°10’ Asymmetric minor fold hinge - bearing and plunge shown brachiopods, and calcareous foraminfera. Maximum thickness 150 m. 63 34 57 sanidine. Biotite crystals several millimeters to ~ 1 cm are rare, and Geological Survey Journal of Research, v. 6, n. 5, p. 579—592. commonly weathered to a copper-brown color. Forms at least two Link, P.K., and Fanning, C.M., 2009, Age and provenance of Precambrian 26 MILLIGEN FORMATION, UNDIVIDED (SILURIAN- Ok distinct subvertically foliated spires within the Challis Volcanic metamorphic rocks in the Pioneer Metamorphic Core Complex, Tei DSm DEVONIAN) – Mainly dark-colored, gray weathering, slabby, 48 000m. Group exposure. Thickness 10-20 m. south-central Idaho: the southern edge of the lower Belt Supergroup, 47 N 28 phyllitic to subphyllitic argillite and black, thin-bedded to massive, 45 the Grouse Creek block, and hints of a proximal Grenville source in DSm 48 000m. carbonaceous to siliceous, cherty argillite. Subordinate interbeds of 47 N ANDESITE BLOCK AND ASH FLOW – Dark-gray, purplish the northern Cordillera: Geological Society of America Abstracts with 729 gray, poorly sorted, fine-grained quartzite, reddish-weathering Tcba weathering blocks of andesite lava in clay-altered, ashy matrix. Programs, v. 41, n. 7, p. 271. 38 dolomitic siltstone, and thin beds of blue-gray, silty, micritic to Blocks are radially fractured, 10-50 cm in size containing green Mahoney, J.B., Link, P.K., Burton, B.R., Geslin, J.K., O’Brien, J.P., 1991, Qg Oe granular bioclastic limestone occur in the lower part. Chert-quartzite Tcl 63 Qal weathering rinds and chlorite alteration along radial fractures; Pennsylvanian and Permian Sun Valley Group, Wood River Basin, 85 granule to pebble conglomerate is common in the upper part. Upper 7 33 contains rare, large (2-3 cm) plagioclase laths. Thickness approxi- south-central Idaho in Cooper, J.D., and Stevens, C.H., eds., Paleozoic 23 and lower contacts both faulted; internal deformation complex. mately 300 m. paleogeography of the Western United States—II: Los Angeles, 36 Phyllitic foliation and crinkle cleavage are common and related to Tci 36 42 Pacific Section Society of Economic Paleontologists and 89 83 major internal folds. Aggregate minimum thickness of 1,200 m. Qc 41 ANDESITE LAVA FLOW – Discontinous outcrops of reddish-brown Mineralogists, Publication 67, v. 2, p. 551—579. PIPw6 Ok Description from Dover (1983). 48 69 Tca 46 71 weathering, dark-gray, fine-grained lava flow. Contains abundant Turner, R.J.W., and Otto, B.R., 1988, Stratigraphy and structure of the 35 63 61 28 43 61 72 clay-weathered hornblende (?). Low temperature alteration indicated Milligen Formation, Sun Valley area, Idaho in Link, P.K., and Hackett, MILLIGEN FORMATION, CAIT QUARTZITE MEMBER 41 4846 by assemblage of quartz-chlorite-epidote-zeolite. Rarely, ~ 1 cm-size W.R., eds., Guidebook to the geology of central and southern Os DScq (SILURIAN-DEVONIAN) – Well-exposed, coarse-grained dark gray crystals of plagioclase and skeletal olivine are present. Thickness Idaho: Idaho Geological Survey Bulletin 27, p. 153-167. Ok quartzite and interbedded black argillite. Contains well-rounded Qc 70 79 approximately 5-10 m. 31 74 66 quartz grains ~1 mm in size. Discontinuous exposures, outcrops as 38 ACKNOWLEDGEMENTS 59 single beds a 0.5-4 m thick and in sequences as thick as 100 m 61 Tei FEEDER DIKES – Subvertically foliated, intermediate (dacitic to This project was supported by the National Science Foundation under 79 Qc Tci composed of beds 10 m thick. Description from Turner and Otto andesitic) porphyritic hypabyssal intrustions; heavily sericticized. Grant No. 0838476 and the U.S. Geological Survey under EDMAP grant (1988). 70 IPw5 66 Occur as meter-scale lenses, discontinuous over 10-15 m. #G10AC00323. The authors would like to thank the landowners in the East PIPw6 Os 47 Fork Wood River Valley for granting access. Thanks to Diana Boyack for 55 MILLIGEN FORMATION, LOWER ARGILLITE (SILURIAN- 4845 730 PIONEER INTRUSIVE SUITE (EOCENE) – Non-foliated, light- her patience and assitance during digitization. Special thanks to Lee Hess, Tei DSla DEVONIAN) – Black, carbonaceous to siliceous, locally phyllitic Tcba gray, medium-grained porphyritic hornblende-biotite quartz monzo- Angela Lexvold, and Jim Vogl for their invaluable field work. Tcp 49 PIPw6 argillite, containing interbeds of dark, poorly sorted, impure quartzite Tcba 48 nite; occurs in small altered bodies. Sharp cross-cutting contacts with 45 and gritty quartzite. Contains interbeds of gray, buff- to orange- wallrocks, which show weak to nonexistent contact metamorphic IPw4 weathering, calcareous siltstone. Indistinguishable from Milligen PIPw6 70 effects. Description from Dover (1983). Tcl Tcd Formation (Dm) within study area. Thickness at least 200 m, but IPw5 63 30 IPw5 locally faulted. Description from Turner and Otto (1988). 68 Qg WOOD RIVER FORMATION, WILSON CREEK MEMBER 55 65 Os (Descriptions from Mahoney et al., 1991) 739 IPw3/4 43 Tcp IPw3/4 74 64 SATURDAY MOUNTAIN FORMATION (ORDOVICIAN) – 63 Tcd IPwh Os Predominantly dark-gray marble containing disseminated diopside, 15 Os WOOD RIVER FORMATION, MEMBER 7 (PERMIAN) – Thin- PIPw6 graphite, and quartz. Upper part mainly alternating thin to medium 4844 DSm IPw3/4 IPw5 Pw7 bedded, dark-gray to black carbonaceous and calcareous siltstone Qg beds of light-gray, fine-grained, diopside-rich marble and darker, Tei Tca 71 65 31 53 with parallel laminations; contains base-cut-out Bouma sequences; 82 Tcl Qc Qt 58 more-graphitic beds of coarse calcite marble. Lower part more 48 interbeds of bluish-gray silty to sandy micrite, cherty micrite, and DSm 69 44 coarsely crystalline, massive, acontains thin siliceous stringers. Top micritic siltstone containing parallel and convolute laminae, graded truncated by faults; lower contact sharp and concordant. Minimum 50 IPwh bedding, soft-sediment deformation, and biotrubation. Contains 70 59 Os thickness of 240 m. Description from Dover (1983). 45 70 48 Tcl fusulinids. Occurs mainly as subcrop on hillsides. Minimum thick- 44 DSm 48 DSm Qc 66 44 IPw5 39 Qal Qt Qc 79 Qt ness of 1,000 m. Qc 31 Tcr IPwh DSm KINNIKINIC QUARTZITE (ORDOVICIAN) – White, pink, Qal Ok PIPw6 19 DSm 731 Ok A Qg 3171 II NW 3171 II NE yellow-brown, or mottled-gray vitreous quartzite; distinguished from 61 (HYNDMAN PEAK) (GRAYS PEAK) IPwh DSm 11 other quartzites in the metasedimentary sequence by its purity (~99% 114°02’30” Tcba 43°42’30” 43°42’30” 58 30 quartz). Rare, thin muscovite partings, locally faintly laminated. 4843 65 48 114°07’30” 43°42’30” Ok 48 43°42’30” 37 Oe 7 Original texture is fine grained, well-sorted, with subrounded quartz IPw5 Tcd IPw5 32 27 IPw3 IPw4 54 724 30 Oe grains; commonly masked by recrystallization to coarser interlocking IPw4 Qg 34 64 34 64 48 quartz crystals, which are locally elongated and boudined. Upper 3 m IPw5 59 43 733 39 55 CZbc 20 43 18 of unit is cross-bedded and coarser-grained. Thickness 90-150 m. 738 Qc 45 78 74 CZbc Description from Dover (1983). 4843 Qc Qg 56 7 48 Tcr Qg 21 34 43 IPw4 Qt Oc Tca 57 735 114°05’ 78 43 DSm 63 Tci 14 Ok IPwh 17 34 59 Oe 7 71 74 44 Oc 36 DSm 114°12’30” 11 47 54 Ok 737 725 35 49 79 38 48 IPw4 Tcl 74 PIPw6 52 72 42 DSm Qc CZbc 69 18 DSm Qt 36 54 14 11 32 Qt 64 Tci 76 Qt Tci 74 IPwh Tci IPw5 CORRELATION OF MAP UNITS 56 Oc IPw5 DSm 49 IPw3 DSm 41 PIPw6 48 Ok 54 64 Qal Qc Holocene Oe IPw5 Tci Tci IPwh DSm Oe 73 4842 IPw5 IPw4 Qt 78 Tci 81 68 75 59 Tci Qg Pleistocene 45 66 72 IPw3/4 40 Tci IPwh 69 PIPw6 Unconformity 7 61 80 Hanging wall, Wildhorse Footwall, Wildhorse 26 Qc 63 Ok 53 55 detachment fault system detachment fault system 50 IPw5 41 55 61 76 80 55 62 4841 Qc IPwh Tci 59 67 PIPw6 37 68 Tcr Tci Qt Qal 40 50 73 53 Qg Tcd 30 49 48 47 37 58 A’ 78 CENOZOIC 67 48 85 41 42 Tcl 42 53 7 Tcu Tci Early to Middle 27 85 Eocene IPw3 IPw4 Tcp Tci 7 71 39 33 54 Tci 62 48 52 Tcba Tei 41 IPw3/4 49 4840 Tca 62 62 CHALLIS VOLCANIC GROUP CHALLIS 45 49 69 55 Unconformity 43 IPwh Qc Pw7 Early 54 75 63 Tci Permian 7 39 DSm 66 PIPw6 member 28 48 4840 71

Wilson Creek Wilson PIPw6 71 66 DScq 57 58 114°02’30” IPw5 51 114°10’ 48 Late 53 Pennsylvanian 76

member IPw4

Eagle Creek 75 IPw3/4 63 59 IPw3 35 60 4839 53 7 53 29 11

WOOD RIVER FORMATION Middle IPwh IPwh 57 62 59 42 Hailey Pennsylvanian member 7 64 7 Unconformity 30 53 38 44 63 4839 Middle PHI KAPPA MOUNTAIN Map Location 7 000m. 43°40’ DSm 31 N 43°40’ 49 IPw5 Devonian 49 DScq Early 732 7 Devonian 114°07’30” DSm 57 37

MILLIGEN DSla DSm Late 3171 II NW 3171 II NE FORMATION PALEOZOIC (HYNDMAN PEAK) (GRAYS PEAK) 7 Silurian 33 48 Unconformity 38 72 48 736 Middle to Late 38 This Technical Report is a reproduction of a map originally submitted as part Os GRAYS PEAK 734 735 114°05’ Ordovician HYNDMAN PEAK of a master's thesis. It's content and format may not conform to IGS GN MN standards. Ok 2°02’ Early to Middle 36 MILS Diedesch,Timothy, 2011, Kinematic analysis of the Wildhorse detachment Oe 18° fault system, Pioneer Mountains, south-central Idaho (MS thesis): Idaho Ordovician SCALE 1:24 000 320 MILS State University, Pocatello, ID, 86pp. 1 1/2 0 1 MILE Oc

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET CZbc Neoproterozoic to Cambrian 0 1.5 0 1 KILOMETER

PROTEROZOIC CONTOUR INTERVAL 40 FEET UTM GRID AND 1967 MAGNETIC NORTH NATIONAL GEODETIC VERTICAL DATUM OF 1929 DECLINATION AT CENTER OF SHEET A A’ WEST-NORTHWEST EAST-SOUTHEAST

10,000’ 10,000’ IPw5

IPw4 East Fork Wood River Tcu Qc Trail Creek Fault IPw3/4 IPw5 Johnstone Creek North Fork Hyndman Creek Qg Hyndman Creek IPw4 8,000’ IPw3 8,000’ Oc Qt Qal IPwh IPw4 Tcu Qc IPw3/4 PIPw6 Qt Qal IPw5 Qal Oe DSm Oc IPwh IPw5 IPw4 Wildhorse Detachment Fault Oe DSm Trail Creek Fault IPwh Lake Creek Fault Ok 6,000’ 6,000’ Elevation

White Mountains Fault DSm Os DSm

DSm 4,000’ 4,000’ Ok

Oe

Oc CZbc 2,000’ 2,000’ 1:24,000 No Vertical Exaggeration Subsurface Geology Modified from Dover, 1983 1- Department of Geosciences, Idaho State University, Pocatello, ID 83209-8072, USA

Published and sold by the Idaho Geological Survey University of Idaho, Moscow, Idaho 83844-3014